Controlled deflection brakes according to WO 98/05812, U.S. Pat. No. 4,962,976 A and EP 0 239 055 A are used in insertion systems of different weaving machine types, e.g. jet weaving machines, gripper or rapier weaving machines, etc., for controlling the weft yarn insertion in view of a minimum quota of yarn breakages or fabric faults, respectively. The weft yarn is deflected during braking by means of a pivotable or lineally moveable braking element which is adjusted between a passive position without any braking effect and a deflecting braking position.
WO 98/05812 discloses a selection of braking functions of a deflection brake for a jet weaving machine. During a first part of an insertion, the rotatable braking element remains in its passive position without influence on the weft yarn flight. In the final part of the insertion and when an unavoidable whiplash effect caused by the activation of the stopping device of the feeder would cause a yarn tension peak, the braking element is adjusted into its braking position to attenuate the yarn tension peak. The braking force first is adjusted such that the braking element resiliently is brought back by the yarn from its braking position in a direction towards its passive position in order to dissipate energy. After this point in time, the braking force is decreased such that during the subsequent weft yarn beat up action of the reed, the yarn length stored in the deflection brake is released and the yarn is kept stretched out. In this situation, the braking element at least substantially returns in its passive position before the weft yarn is cut. Since the cut weft yarn is loaded by a holding force generated by the insertion nozzle, the decreased braking force just should suffice to again adjust the braking element into its braking position and to pull back the free weft yarn tip into the insertion nozzle. Then, for the next insertion the braking element is adjusted back into its passive position. In a gripper or rapier weaving machine different braking functions are needed than in a jet weaving machine. Basically, it can be said for a controlled deflection brake that its performance is the better the more accurately at least two functional parameters are adapted to the weaving operation conditions, namely the braking force and the point in time of the brake activation. WO 98/05812 discloses to time or regulate the activation point in time of the deflection brake and its braking force, respectively, that the curve of the supplied current is matched with conditions or parameters depending on the yarn quality, the weaving machine type and the mode of operation of the system, and that the response behaviour of the deflection brake and certain delay times are considered. However, it is not explained how such regulations are made. In practice, such parameters are adjusted with the help of a yarn tension measuring device arranged in the yarn path between the deflection brake and the insertion nozzle. A tensiometer provided in the yarn path for such purposes, however, undesirably modifies the yarn flying time, since eyelets and the additional deflection angles of the tensiometer disturb the yarn flight. A tensiometer cannot be implemented permanently, because it is too costly and too sensitive and disturbs the insertion cycles and yarn threading procedures. The method employed in practice, furthermore, is a coarse trial and error process leading to a compromise adjustment of the deflection brake performance only. It does not does not allow an automatic and real time adjustment depending on the actual operation conditions.
It is an object of the invention to provide a deflection brake and a method, as mentioned above, by means of which the yarn insertion is optimised with optimal short weft yarn flight times and a small quota of yarn breakages or fabric faults. Part of the object is an automatic adaptation of the following functional parameters to the actual operation: time of actuation of the deflection brake and the braking force.
Said object can be achieved in a deflection brake having a position detection assembly connected to an adjusting device which correlates with functional parameters of the deflection brake.
The core of the invention is the recognition that the position of the braking element and/or the movement behaviour of the braking element at significant points in time or during significant time durations of an insertion by nature is delivering information on the performance of the deflection brake and is offering a possibility for a simple optimisation of the adjustments, without the necessity of mechanical interference by measuring instruments which disturb the yarn flight. An optimisation of the adjustment of the brake on the basis of the respective position of the braking element leads to optimally short weft yarn flight times, to minimum variations of the weft yarn flight times, to a minimisation of the energy consumption of the deflection brake and of other components of the insertion system consuming energy and the like.
A “point in time or time duration” can be expressed by a certain angle value or angle range of the rotation e.g. of the main shaft of the weaving machine as well. The term “braking force” is equal with the actuating force or the braking torque of the braking element or its drive motor, respectively.
The position detection means of the deflection brake generates information of the initial position and/or the momentary movement behaviour of the braking element by comparison with a target position and allows an adaptive optimisation of the functional parameters by the adjustment device. No measuring instruments are needed which could mechanically disturb the yarn flight. The performance of the deflection brake is checked exactly and varied at the location where during operation the deflection brake is engaging the weft yarn.
According to the method of the invention, target positions of the braking element are set beforehand for selected times during an insertion. By means of the respective actual detected positions of the braking element detected during the insertion, differences between the target positions and the actual positions can be determined and can be converted into correction signals. Based on correction signals, the functional parameters are adjusted. This leads to an adaptive optimisation control of the performance of the deflection brake for an optimal weft yarn insertion.
The position detection means should have at least one position indicator moving with the braking element and a stationary position detector, both coacting without mechanical influence on the weft yarn, while providing the required information.
A structurally simple solution incorporates a permanent magnet at the braking element. The magnetic field of the magnet is scanned by an analogously operating Hall effect sensor. In this case, at each selected time the position of the braking element will be known. Alternatively, the movement behaviour of the braking element can be determined within a selected time duration. Said information is used for the optimisation.
Expediently, the control device is in signal receiving connection with one or several components of the weft yarn insertion system, which components are apt to give additional information for the selected times.
According to the method, by using the position information of the braking element and in case that the deviations from the target positions are detected, the mentioned functional parameters are varied in view of a duration of the weft yarn flight time which is an optimum for the weaving machine.
Particularly in a jet weaving machine the mentioned functional parameters of the deflection brake are the timing of the brake actuation or de-actuation and/or the braking force. This should not exclude varying other functional parameters, e.g. in other types of weaving machines.
Selected times or points in time can be determined by means of winding unspooling signals of a sensor of the feeder which signals follow the yarn during the course of the insertion.
Other relevant points in time correlate with the occurrence of activating and/or de-activating signals of the weft yarn stop device of the feeder.
Even the occurrence of a weft yarn cut signal represents a relevant point in time for a check of the function of the deflection brake.
Basically, and according to the method the inherent response behaviour of the deflection brake for activating and de-activating signals or braking force variation signals ought to be considered.
According to a variant of the method it is determined whether or not the deflection brake is operating as intended at the point in time of the unavoidable yarn tension peak initiated by the engaging stopping device of the feeder. If the braking element at this point in time still remains in the braking position, even though it should have left the braking position to attenuate the yarn tension peak, the braking force is decreased such that the deflection brake will have a better performance during a later insertion.
Furthermore, it is checked according to the method at the point in time of the yarn tension peak whether or not the braking element carries out oscillating position changes during a predetermined time duration, because this indicates a too weak braking force. If yes, the braking force is increased to achieve a better performance during a later insertion.
If according to the method it is determined that the braking element has not yet reached the target braking position at the point in time of the yarn tension peak, this indicates that the deflection brake had been activated too late. Then the point in time for the activation is adjusted to “earlier”, in order to create improved conditions for later insertions.
Furthermore, according to the method a detected braking position of the braking element prior to the point in time of the yarn tension peak indicates that the deflection brake has been activated too early and would brake the weft yarn too long (prolongation of the weft yarn flight time). This detection result is used to adjust of the point in time of the brake actuation to “later” to achieve a better function for a later insertion.
In case that the braking element has not moved into or at least close to the target passive position at the point in time of the cut signal, this indicates a momentary braking force which is too high, thereby jeopardising the needed pull back function. As a consequence, the braking force then will be decreased.
After occurrence of the cut signal, the holding force of the insertion nozzle is still acting on the cut weft yarn. The braking force then should be just enough to overcome the holding force. By respectively increasing and decreasing the braking force in depending upon whether or not the braking element then reaches the target braking position too rapidly or not at all, the braking force is adjusted and adapted to the momentary holding force of the insertion nozzle. By carrying out such steps, both the holding force and the braking force can be adjusted optimally low in order to save energy for the actuation of the deflection brake and fluidic energy for the insertion nozzle.
The detection of the actual positions of the braking element or the movement behaviour of the braking element, comparisons with the target positions, derivations of correction signals and adjustments of the functional parameters are carried out substantially in real time so that even with very high yarn speeds and high insertion frequencies of modern weaving machines a permanent adaptive adjustment of optimum operation conditions of the deflection brake is achieved without additional mechanical yarn disturbance.
The above described method variants are only a selection of a greater plurality of possibilities, e.g. appropriate for air jet weaving machines, even though e.g. in other weaving machine types there might exist other points in time or angles during an insertion at which the position or the movement behaviour of the braking element can give clear information on the performance of the deflection brake to adaptively optimise its performance.